1. Field of the Invention
The present invention relates to a back pressure control valve for controlling fluid (liquid or gas) on a primary side to be in a predetermined pressure condition.
2. Description of the Related Art
In manufacturing semiconductors, it was conventionally performed that for the purpose of keeping pressure of fluid constant at a use point utilizing agents or ultrapure water, a pressure adjusting valve 70 as shown in FIG. 8 is provided as a safety valve (relief valve) on a downstream side of the use point of a fluid circuit for controlling (or keeping) the fluid on a primary side (upstream side) of the pressure adjusting valve 70 to be in a predetermined pressure condition.
The above-described conventional pressure adjusting valve 70 is comprised of a body 71 including a first chamber having an inlet portion 73 for controlled fluid that is connected to the fluid circuit, a second chamber 74 having an outlet portion 75 for the controlled fluid, and a communicating flow path 76 for fluid communication between the first chamber 72 and the second chamber 74 and being formed with a valve seat 77, and further of a valve mechanism 80 including a valve portion 81 for opening and closing the valve seat 77 and being located on the first chamber 72 side of the communicating flow path 76, and a diaphragm portion 82 which is arranged within the first chamber 72, wherein an outer peripheral portion 83 of the diaphragm portion 82 is fixed to the body 71, and the first chamber 72 is divided into a valve chamber 91 including the inlet portion 73 inside the diaphragm portion and a pressure adjusting chamber 92 outside the diaphragm portion. In the pressure adjusting chamber 92, a pressure adjusting means 93 such as pressure adjusting gas (as used in this example of the drawing) or a spring adjusts a pressure of the diaphragm 82 to be a predetermined pressure to keep the diaphragm portion 82 in a predetermined direction (downward in the drawing, which is a direction of the valve chamber). In the drawing, reference numeral 94 designates a supply gas port for the pressure adjusting gas, while reference numeral 95 designates an exhaust port.
In the back pressure control valve 70, the pressure within the fluid circuit, that is, the fluid pressure on the primary side of the back pressure control valve 70 is received by the valve mechanism 80, while an opening degree of the valve seat 77 is controlled by balancing the fluid pressure on the primary side and the set pressure of the pressure adjusting means 93 for pressing the valve mechanism 80 so as to keep the fluid on the primary side in a predetermined pressure condition. More specifically, when pressurizing force of fluid acting on the valve mechanism 80 becomes larger than a pressurizing force of the pressure adjusting means 93, the valve mechanism 80 is moved towards the pressure adjusting chamber (upward in the drawing) to open the seat valve 77 such that the fluid within the fluid circuit is discharged. On the contrary, when the pressurizing force of the fluid acting on the valve mechanism 80 becomes smaller than the pressurizing force of the first pressure adjusting means 93, the valve mechanism 80 is moved towards the second chamber to close the valve seat 77 such that the amount of discharged fluid from the fluid circuit is reduced.
However, the conventional back pressure control valve 70 is not provided with any functions for coping with pressure variation on a secondary side (outlet portion side) accompanying variations in discharge flow rate or the like. Thus, influences caused by pressure variations on the secondary side (for example, limitations in movements of the valve mechanism 80 accompanying the variation) will be of concern. Especially, when the communicating flow path 76 of the body 71 is of large diameter, an area of a pressure-receiving surface 81a on the valve portion side of the valve mechanism 80 will become large so that influences of pressure variations on the secondary side will be remarkable. In addition, the back pressure control valve 70 was mainly used as a safety valve because it was not provided with any functions for coping with pressure variations on the secondary side. Further, when the pressure adjusting 93 is comprised by a spring in the back pressure control valve 70, hysteresis occurs at the time of operating the valve mechanism 80 to result in degradations in repetition accuracy, and a drawback was presented in that the pressure of fluid on the primary side could not be accurately controlled to be a predetermined pressure.
The present invention has been proposed in view of the problems described above, and is directed to provide a structure for a back pressure control valve which exhibits favorable repetition accuracy at the time of operating the valve mechanism, which is capable of accurately controlling pressure of fluid on a primary side (inlet side), and which is not affected by pressure variations on a secondary side.
Moreover, the present invention is further directed to provide a structure for a back pressure control valve enabling new embodiments thereof thanks to the above-described fact that the structure is not affected by pressure variations on the secondary side.
More particularly, the invention as recited in claim 1 of the present invention provides a back pressure control valve (10) for controlling fluid on a primary side to be in a predetermined pressure condition, comprising: a body (11) including a first chamber (12) having an inlet portion (13) for controlled fluid, a second chamber (14) having an outlet portion (15) for the controlled fluid, and a communicating flow path (16) for fluid communication between the first and second chambers and being formed with a valve seat (17), and a valve mechanism including a rod portion (21) with a valve portion (22) for opening or closing the valve seat and being positioned on the first chamber side of the communicating flow path, a first diaphragm portion (30) provided on one side of the rod portion and being arranged within the first chamber, and a second diaphragm portion (40) provided on the other side of the rod portion and being arranged within the second chamber, wherein an outer peripheral portion (32) of the first diaphragm portion is fixed to the body comprising the first chamber, the first chamber being divided into a first valve chamber (51) including the inlet portion inside the first diaphragm portion and a first pressure adjusting chamber (52) outside the first diaphragm portion, wherein an outer peripheral portion (42) of the second diaphragm portion is fixed to the body comprising the second chamber, the second chamber being divided into a second valve chamber (56) including the outlet portion inside the second diaphragm portion and a second pressure adjusting chamber (57) outside the first diaphragm portion, and wherein the first pressure adjusting chamber is provided with a first pressure adjusting means (M1) for adjusting a pressure of the first diaphragm portion to be a predetermined set pressure in a predetermined direction, while the second pressure adjusting chamber is provided with a second pressure adjusting means (M2) for adjusting a pressure of the second diaphragm portion to be a predetermined set pressure in a predetermined direction.
Further, the invention as recited in claim 2 of the present invention relates to the back pressure control valve of claim 1, wherein an effective diameter of the first diaphragm portion is set to be larger than an effective diameter of the second diaphragm portion.
Moreover, the invention as recited in claim 3 of the present invention relates to the back pressure control valve of claim 1 or 2, wherein an effective pressure-receiving area of the second diaphragm is set to be equal to an effective area of the valve seat.